IGMP (Internet Group Management Protocol)

A communication protocol used by IPv4 hosts and adjacent multicast routers to dynamically register and manage IP multicast group memberships (defined in RFC 2236 for version 2 and RFC 3376 for version 3). In the entertainment lighting industry: IGMP is the foundational mechanism that allows networked devices (such as DMX gateways and intelligent fixtures) to subscribe to specific Streaming ACN (sACN) control universes. When a lighting fixture needs to receive data for a mapped universe: it transmits an IGMP Membership Report (commonly known as a Join message) onto the network. Managed switches with IGMP snooping enabled intercept these reports to map multicast addresses to specific physical ports: ensuring sACN data is delivered only to interested devices. To keep this system active and prevent switches from timing out and flooding the network: an IGMP Querier must be active on the network to periodically send queries and verify that receivers are still online.